There are various applications in the semiconductor industry where two substrates in the form of flat panels have to be bonded together. Typically, at least one of the panels would be made of glass. For instance, for producing touch-screen display panels, two glass panels may have to be bonded together. Another common application is where a protective glass layer is bonded onto a semiconductor wafer in the making of solar panels. An adhesive such as epoxy is typically used to seal the two substrate panels together for downstream processing. Some applications such as the production of touch panels generally require relatively lower bonding accuracy, whereas other applications such as the production of liquid crystal display (“LCD”) panels require relatively higher bonding accuracy.
FIG. 1 is a process flow chart which illustrates a conventional bonding sequence for laminating substrates. Separate substrates are first input into a lamination machine 100. The substrates are aligned relative to each other using mechanical alignment 102, that is, there are mechanical features in the lamination machine 100 such as reference stoppers to orientate the substrates relative to each other. An adhesive is dispensed 104 onto at least one of the substrates. Thereafter, lamination 106 is conducted wherein the substrates are bonded to each other, before the laminated substrate is removed from the lamination machine 100.
FIGS. 2a to 2d schematically illustrate a conventional bonding sequence for laminating substrates. First and second substrates 118, 120 are loaded onto respective holding tables 112, 114 of the lamination machine 100. The positions of the substrates 118, 120 are aligned by mechanical features, such as stoppers 116. A dispensing apparatus 121 that can be driven in the X, Y and Z directions will dispense an adhesive resin 122 in a predetermined pattern onto the first substrate 118. A transport device 124 will carry the second substrate 120 to a position above the first substrate 118 such that inner surfaces of the substrates 118, 120 oppose each other. The holding table 112 will be raised relative to the second substrate 120 until a required resin thickness is reached. Then, the holding table 112 will be lowered together with the laminated substrate 126. The laminated substrate 126 will be unloaded and transported to an external curing system 128 where the resin is cured by a curing device 130 in order to bond and secure the laminated substrate 126.
It would be noted that the positions of the separate substrates 118, 120 are guided by mechanical stoppers 116. The placement accuracy will be affected by limitations of mechanical alignment, such as the variations in sizes of the substrates 118, 120 due to imprecise manufacturing.
The problem with the above approach of the prior art is that the bonding accuracy of the panel bonding machines depends mainly on the precision of the guiding jig. That gives rise to inaccuracy because substrate sizes are inconsistent, even among the same production lot. Without the aid of a real-time pattern recognition system to rectify any positional error, the placement quality is difficult to assure since it is sensitive to material variation.